Ion implanting while growing a III-nitride layer

ABSTRACT

A method that includes implantation of dopants while a III-nitride body is being grown on a substrate, and an apparatus for the practice of the method.

RELATED APPLICATION

This application is based on and claims priority to U.S. ProvisionalApplication Ser. No. 60/937,101, filed on Jun. 25, 2007, entitled IonPlanting While Growing A III-Nitride Layer, to which a claim of priorityis hereby made and the disclosure of which is incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to semiconductor device fabrication andmore particularly to III-nitride device fabrication.

DEFINITION

As referred to herein III-nitride refers to a semiconductor alloy fromthe InAlGaN system, including, but not limited to GaN, AlGaN, InAlGaN,AlN, InN, InGaN, and the like.

BACKGROUND OF THE INVENTION

Commercial interest in III-nitride devices is rapidly growing.

A basic problem in III-nitride device fabrication is the retention ofthe stoichiometry of the III-nitride body. Specifically, it is wellknown that at high temperatures (e.g. above 800° C.) nitrogen may escapefrom the III-nitride body resulting in the decomposition of theIII-nitride. Thus, annealing after implantation presents a challenge inthe field of III-nitride device fabrication, which is a technicalbarrier to the well known process of implantation and annealing used toform PN junctions in a semiconductor body.

SUMMARY OF THE INVENTION

The present invention relates to a process for semiconductor devicefabrication, which can address the problem associated with the doping ofa III-nitride body.

Thus, according to the present invention, a III-nitride body is dopedwhile it is grown to obtain a doped III-nitride body, thereby avoidingthe need for a high temperature anneal.

According to one embodiment of the present invention, a suitablesubstrate for the III-nitride body is placed in a reactor chamber forgrowing the III-nitride body (e.g. GaN body). The reactor chamber isequipped with an implanter for implanting any desired species. Forexample, Si can be used if an N-type III-nitride body is desired and Mgcan be used if a P-type III-nitride body is desired. Thus, according tothe present invention, as the III-nitride body is being grown in thereactor chamber it is implanted with the implanter to obtain a dopedIII-nitride body. Therefore, implanting takes place in an annealingenvironment rather than a decomposing environment. In a processaccording to the present invention, the surface of the growing body isat equilibrium with its surrounding. As a result, the surface does notdecompose, while it is annealed.

While the method of growth is not critical to the practice of thepresent invention, each growth method may offer unique advantages overthe others. Thus, the method of growth can be selected as desiredaccording to its unique advantages.

It is known that at least partial vacuum in the reactor chamber may berequired for implanting, while to grow a III-nitride body over asubstrate a certain amount of gas pressure may be required. Thus, theimplanting technique must be coupled with the growth technique.

According to one aspect of the present invention one or more stages ofdifferential pumping can be used to obtain the gas pressure that isnecessary for implanting and growth. This technique essentially relieson the finite conductance of gas molecules in a low pressureenvironment. The preferred pressure when MOCVD is used may be in therange 10-100 Torr, and if MBE is used the preferred pressure may be inthe range 10⁻⁷ to 10⁻¹¹ Torr. If MBE is used there may be no worriesabout neutralization which can occur in MOCVD.

In a method according to the present invention, low energies arepreferred for implanting. Thus, energies less than tens of KeV (e.g.between 100 eV to tens of KeV) may be used with energies in the range offive to ten KeV being most preferred. Also, the implant beam can be aswide as 1/10 micron and not a few nm.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 schematically illustrates an apparatus configured for thepractice of a method according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, an apparatus for the practice of a method accordingto the present invention includes a reactor chamber 10 for receiving asubstrate 12 (e.g. silicon substrate, SiC substrate, III-nitride (e.g.GaN) substrate, sapphire substrate or the like), and an implanterchamber 14. Note that reactor chamber 10 may house also a rotatingplatform 16 on which substrate 12 is placed, and includes an intake port18 to allow for the entry of a reactant gas and an output port 20 forthe exit of reactant gas.

Disposed within implanter chamber 14 is an ion implanter 22 incommunication with reactor chamber 10 through an ion path 24, which isthe path along which ions travel from the implanter 22 into reactorchamber 10.

According to an aspect of the present invention, implanter chamber 14 isconfigured for maintaining a near vacuum condition within the enclosedspace thereof. Near vacuum condition as referred to herein means avacuum condition necessary to allow passage of ions through the enclosedspace of implanter chamber 14 into reactor chamber 10. In order toobtain such a near vacuum condition while allowing implanter chamber 14to be in communication with reactor chamber 10, differential pumping maybe used to evacuate implanter chamber 14. For one embodiment, forexample, implanter chamber 14 may be divided into several subchambers14′, 14″, 14′″. Each subchamber 14′, 14″, 14′″ is in communication withan adjacent subchamber through a respective portal 26. Note that ionpath 24 passes through each portal 26, and subchamber 14′″, which isadjacent reactor chamber 10, is linked to reactor chamber 10 through alinking portal 28 through which ion path 24 also passes.

To create the near vacuum condition each subchamber 14′, 14″, 14′″ ispreferably evacuated using a respective pump 30. Each pump 30 ispreferably in direct communication with the space enclosed by arespective subchamber as illustrated schematically by FIG. 1.

An apparatus according to the present invention may further include aFaraday cup 32 which may be disposed on platform 16 near substrate 12.Faraday cup 32 is preferably linked to a voltage meter or the likethrough appropriate means such as wires 34 so that the variation in thevoltage thereof can be used to measure the dosage of ions being receivedfrom implanter 32 by substrate 12.

An apparatus according to the present invention may further include aplurality of deflection plates 36 positioned inside reactor chamber 10on either side of portal 28. Deflection plates 36 can be used to changethe direction of travel of the ions entering reactor chamber 10. Notethat deflection plates 36 may be used to direct the ions at Faraday cup32 periodically (e.g. 1% of the time) in order to measure the ion dosagebeing directed at substrate 12 in order to estimate the concentration ofdopants implanted therein.

According to an embodiment of the present invention, a suitablesubstrate 12 (e.g. a silicon substrate) is placed on platform 16 insidereactor chamber 10. Reactant gas is then fed through intake port 18, andthermal conditions are set for the growth of a III-nitride body such asGaN, AlN, or the like. In addition, through differential pumping,subchambers 14′, 14″, 14′″ are evacuated until a suitable, near vacuumcondition is obtained inside implanter chamber 14. The near vacuumcondition may depend on the type of growth that is being practiced. Forexample, if III-nitride is being grown using MOCVD the pressure insideof implanter chamber 14 may be in the range of 10-100 Torr, or if MBE isused for growing the III-nitride body 10⁻⁷ to 10¹⁻¹¹ Torr may be thepressure inside implanter chamber 14.

Once proper pressure is established in implanter chamber 14, any desiredspecies may be implanted into the III-nitride body as it is being grownlayer by layer. Thus, N-type dopants such as Si and P-type dopants suchas Mg may be implanted.

According to one aspect of the present invention, to implant dopants,energies less than tens of keV (e.g. between 100 eV to tens of keV) areused for implantation. Preferably, energies in the range of five to tenkeV are used during the implantation.

Moreover, the implant beam can be as wide as 1/10 microns wide not justa few nm. Note that according to an aspect of the present invention. Thelow energies are used in order to implant the dopants near the surfaceduring the growth process (e.g. 50-200 Å depth) into the grownIII-nitride body. The III-nitride body can be doped to anyconcentration, for example, the III-nitride semiconductor body can bedoped with an ion dose in the range of 10¹²/cm² up to 10¹⁶/cm², with adose of 10¹⁴ to 10¹⁵ being preferred.

According to another aspect of the present invention, the dosage ofimplants is measured to determine the concentration of dopants in theIII-nitride body as it grows.

For example, to calculate the dose the number of electrons emitted canbe counted. This technique may be most suitable for MBE.

In an alternative technique, the ion beam can be sampled 1% of the timeby using a Faraday cup 32 residing on or near the substrate. Deflectionplates can be used in the measurement of ion implantation. Faraday cup32 on the wafer can be used to sample the charge that is implanted.However, negative ions may escape after implantation. To alleviate thisproblem a negative cover may repel the negative charge to get a betterreading. Note that deflection plates (if used) should be positionedafter the differential pumps.

A process according to the present invention can be used to dope theentire III-nitride body that is being grown on the substrate or it canbe used to dope selected regions in the III-nitride body. Thus, to dopeselected regions a metal mask can be used to allow doping only ofregions not covered by the mask. For example, a projection ion beam maskor a stencil with parallel ion beams can used.

Alternatively, a direct writing rastering technique may be used. Todirectly write, a highly focused beam can used to implant selectedregions without using a mask.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

1. A method of fabricating a doped III-nitride semiconductor body,comprising: placing a substrate in a reactor chamber; pumping reactantgas for growing said III-nitride semiconductor body into said reactorchamber; and implanting ions from an implanter, disposed in an implanterchamber in communication with said reactor chamber, into saidIII-nitride semiconductor body to dope said III-nitride semiconductorbody as said III-nitride semiconductor body is continually grown, saidimplanter chamber separate from said reactor chamber, and said implanterchamber comprising a plurality of subchambers; wherein said ions passthrough a space under a near vacuum prior to reaching said substrate. 2.The method of claim 1, wherein said near vacuum is obtained throughdifferential pumping of said space.
 3. The method of claim 1, whereinsaid space is said implanter chamber that further includes an ion pathextending from said implanter to said reactor chamber, said ion pathbeing in communication with said reactor chamber.
 4. The method of claim1, further comprising measuring a dosage of said ions while implantingtakes place.
 5. The method of claim 4, wherein said dosage is measuredusing a Faraday cup.
 6. The method of claim 1, further comprisingchanging a direction of travel of said ions.
 7. The method of claim 6,wherein deflection plates are used to change direction of travel of saidions.
 8. The method of claim 1, further comprising implanting said ionsthrough a metal mask.
 9. The method of claim 1, wherein said ions areimplanted through rastering.
 10. An apparatus for fabrication of a dopedIII-nitride semiconductor body, comprising: a reactor chamber to receivea substrate and reactant gas to grow a III-nitride semiconductor body onsaid substrate; an implanter disposed in an implanter chamber that is incommunication with said reactor chamber to implant ions into said111-nitride semiconductor body and to dope said III-nitridesemiconductor body during the growth of said III-nitride semiconductorbody, said implanter chamber separate from said reactor chamber, andsaid implanter chamber comprising a plurality of subchambers; and atleast one pump coupled to said implanter chamber configured to create anear vacuum condition in said implanter chamber.
 11. The apparatus ofclaim 10, wherein said at least one pump performs differential pumping.12. The apparatus of claim 10, further comprising a Faraday cup disposedwithin said reactor chamber.
 13. The apparatus of claim 10, furthercomprising deflection plates to change the direction of travel of saidions.